Characteristics and control technology of breathing phenomenon of sealed goaf in low-gas mine

After the mining face of low-gas mine is sealed,a large number of free gas gathers in the sealed space. When the quality of the seal drops to a certain extent,the fluctuation of the air pressure out of the sealed goaf will cause “breathing” phenomenon and lead to the gas concentration of the seal’ s outside exceed safety limit. No. 14-1103 sealed goaf of Zhengli Coalmine is selected as the research object,the variation law on inner and outer pressure of sealed goaf and gas concentration of the seal’s outside are analyzed under different atmospheric parameters. The mech- anism of “breathing” phenomenon is theoretically analyzed with ventilation energy equation and state equation of ideal gas,and the expression of relationship between differential pressure and gas concentration is obtained with Darcy law. The results show that,“breathing” phenomenon results from the combining action of ground atmospheric parameters, airflow parameters,roadway characteristics and gas state parameters of sealed goaf. Under the continuous action of dif- ferential pressure between seal’s inside and outside,gas exchange will occur between sealed goaf and outside space. The gas pressure in sealed goaf is gradually decreasing or increasing as the differential pressure is positive or negative. The gas pressure in sealed goaf has small change,the fluctuation of static pressure of the seal’ s outside is the domi- nant factor that results in positive and negative alternation of differential pressure. The variation trend of the static pres- sure of the seal’s outside is similar to that of the ground atmospheric pressure and opposite to that of the ground at- mospheric temperature when roadway characteristics and air quantity are stable. On the premise that the seal’s perme- ability and the air quantity of seal’s outside are relatively stable,the gas concentration is positively correlated with the differential pressure when the positive differential pressure appears,so that,the change trend of gas concentration is similar to that of differential pressure. An automatic control system of gas release,which consists of monitoring signal acquisition subsystem,field automatic control subsystem and pipeline explosion suppression subsystem,is designed to prevent gas concentration of seal’s outside from exceeding safety limit. The joint control criteria is determined based on the threshold values of differential pressure and gas concentration,and the grading control logic of valve opening is put forward.